Method and device for producing carbon nanotubes

ABSTRACT

Methods and devices for producing carbon nanotubes are disclosed herein. These methods and devices are based on chemical vapor deposition (CVD) in an open environment under atmospheric pressure, which eliminates the need for a vacuum chamber or evacuation process to remove oxygen and/or impurities prior to carbon nanotube growth.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

The United States Government has certain rights in this inventionpursuant to National Science Foundation Grant No. CTS 0093544.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application relates to, and claims the benefit of, U.S.Provisional Patent Application No. 60/683,627, which was filed on May23, 2005, and is incorporated herein in its entirety.

BACKGROUND

This disclosure relates generally to carbon nanotubes and, morespecifically, to a method and device for producing carbon nanotubes inopen environments.

Carbon nanotubes (also referred to as carbon fibrils) have received muchattention owing to their promising electronic and mechanical properties.The nanotubes can be thought of as rolled up sheets of graphite, whichmay be open or capped at each end. Measurements have shown that theirdiminutive size belies a host of practical applications, such asmolecular wires, transistors, nanoswitches, diodes, chemical sensors,high strength materials, electron field emitters, and tips for atomicforce microscopes, among others. Carbon nanotubes are metallic,semimetallic, or semiconducting depending on their diameter and thehexagonal pattern along the tube axis (i.e., their chirality). They arealso extremely strong, with a Young's Modulus similar to diamond andsignificantly greater than most known metals and alloys.

Presently, there are three main approaches towards the synthesis ofcarbon nanotubes. These include electric arc discharge of graphite,laser ablation of graphite, and chemical vapor deposition (CVD) ofhydrocarbons. The arc discharge and laser ablation techniques involverather extreme conditions (e.g., temperatures greater than about 3000°C.), with low nanotube yield. CVD methods have emerged as viablealternatives because, in part, they have shown that milder conditionsare feasible and that bulk (e.g., kilogram or even ton) quantities ofcarbon nanotubes can be produced. Other techniques, which are in theirearly stages of development and will require much effort in order toovercome the technical challenges for mass production of carbonnanotubes, include open-air flame synthesis of carbon nanotubes and atemplate synthesis technique. The template synthesis technique hassuccessfully been used to grow vertically-aligned carbon nanotubearrays; however, this technique leads to the formation of structuralirregularities and defects.

There are several drawbacks associated with existing CVD processes. Forexample, the relatively low deposition temperature (e.g., less thanabout 1200° C.) results in carbon nanotubes with high defectconcentrations and lower degrees of graphitization compared to thosegrown by arc discharge and laser ablation techniques. Additionally,deposition rates for CVD techniques are generally limited to about 10micrometers per minute, and the cost of nanotubes can range from 60-750dollars per gram, which is more expensive than gold. Finally, highvacuum growth chambers are needed in order to eliminate oxidation ofas-grown carbon nanotubes, which complicates the synthetic procedure andincreases the overall cost of the equipment.

There accordingly remains a need in the art for new and improved methodsand devices for producing carbon nanotubes. It would be particularlydesirable if these methods and devices provided the advantages of CVDover arc discharge and laser ablation while simultaneously offeringperformance advantages (e.g., lower defect concentrations, higherdegrees of graphitization, higher deposition rates, less complicatedprocedures, and/or lower equipment costs) over existing CVD methods.

BRIEF SUMMARY

A device for producing carbon nanotubes includes a fluid deliveryportion comprising a carbon-containing precursor reservoir, a reducingagent reservoir, and an inert gas reservoir; a coaxial jet reactor influid communication with the fluid delivery portion, wherein the coaxialjet reactor comprises an outer nozzle configured to receive an inert gasand an inner nozzle configured to receive a carbon-containing precursorand a reducing agent; a deposition portion in fluid communication withthe coaxial jet reactor, wherein the deposition portion comprises anouter zone configured to receive the inert gas from the outer nozzle, aninner zone configured to receive the carbon-containing precursor andreducing agent from the inner nozzle, and a substrate having at least aportion within the inner zone, wherein the outer zone, inner zone andthe substrate are in an open environment; and a heating sourceconfigured to heat at least the portion of the substrate within theinner zone effective to thermally decompose at least a portion of thecarbon-containing precursor in the presence of the reducing agent andproduce the carbon nanotubes on the substrate.

In another embodiment, the device for producing carbon nanotubesincludes a fluid delivery portion comprising a carbon-containingprecursor reservoir, a reducing agent reservoir, an inert gas reservoir,a carbon-containing precursor mass flow controller, a reducing agentmass flow controller, an inert gas mass flow controller, and a mixer ata junction downstream of the carbon-containing precursor reservoir andthe reducing agent reservoir, and a coaxial jet reactor in fluidcommunication with the fluid delivery portion, wherein the coaxial jetreactor comprises an outer nozzle configured to receive an inert gas andan inner nozzle configured to receive a carbon-containing precursor anda reducing agent; a deposition portion in fluid communication with thecoaxial jet reactor, wherein the deposition portion comprises an outerzone configured to receive the inert gas from the outer nozzle, an innerzone configured to receive the carbon-containing precursor and reducingagent from the inner nozzle, a substrate having at least a portionwithin the inner zone, a nanotube growing catalyst disposed on a surfaceof the substrate, an exhaust, and a scattered light absorber, whereinthe outer zone, inner zone, substrate, nanotube growing catalystexhaust, and scattered light absorber are in an open environment; alaser, wherein a beam produced by the laser is configured to heat the atleast the portion of the substrate within the inner zone effective tothermally decompose at least a portion of the carbon-containingprecursor in the presence of the reducing agent and produce the carbonnanotubes on the substrate; and a controller in operative communicationwith the laser, carbon-containing precursor mass flow controller,reducing agent mass flow controller, inert gas mass flow controller,mixer, substrate or a combination comprising at least one of theforegoing.

A method for growing carbon nanotubes includes heating at least aportion of a substrate in an open environment; forming a first jet ofreactants comprising a carbon-containing precursor and a reducing agent,wherein the first jet is surrounded by a second jet of inert gas that iseffective to protect the reactants from the open environment; thermallydecomposing at least a portion of the carbon-containing precursor in thepresence of the reducing agent in proximity to the heated substrate; andgrowing the carbon nanotubes on the at least the portion of thesubstrate.

The above described and other features are exemplified by the followingfigures and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the Figures, which are exemplary embodiments, andwherein the like elements are numbered alike:

FIG. 1 is a schematic representation of an open environment chemicalvapor deposition device;

FIG. 2 is a schematic representation of a moving substrate device;

FIG. 3 illustrates environmental scanning electron microscope (ESEM)images of (a) 80 nanometer and (b) 300 nanometer gold-palladium catalystparticles disposed onto a 3 millimeter fused quartz rod substrate; and

FIG. 4 illustrates ESEM images of carbon nanotubes of (a) 50 nanometerand (b) 220 nanometer diameters deposited onto a 3 millimeter fusedquartz rod substrate.

DETAILED DESCRIPTION

Chemical vapor deposition (CVD) methods and devices for making carbonnanotubes are described herein. In contrast to the prior art, themethods and devices are based on chemical vapor deposition under openenvironment conditions, which provide several advantages over existingcarbon nanotube production methods and devices. For example, depositionof the carbon nanotubes occurs under atmospheric pressure, whicheliminates the need for a costly vacuum chamber and therefore atime-consuming evacuation process to remove oxygen and/or impuritiesprior to deposition. In addition to the elimination of this processstep, open environment CVD allows for deposition rates that may be up tothree orders of magnitude greater than other CVD techniques. Otheradvantages of open environment CVD based methods and devices will beapparent to those skilled in the art in view of this disclosure. It isto be understood that “open environment”, as used herein, may includethe use of an exhaust, vent, or the like.

As used herein, the term “carbon nanotube” is inclusive of a variety ofcarbon fibers having average diameters of less than or equal to about2000 nanometers (nm) and having graphitic or partially graphiticstructures. These include semiconducting, semimetallic, and metallicnanotubes as well as single-walled nanotubes (SWNT) and multi-wallednanotubes (MWNT). They may have lengths of a few nanometers to manycentimeters. Furthermore, each carbon nanotube may be derivatized orfunctionalized, for example including an oxygen-containing group such asa carbonyl, carboxylic acid, carboxylic acid ester, epoxy, vinyl ester,hydroxy, alkoxy, isocyanate; amide group; or derivatives thereof, forexample, sulfhydryl, amino, or imino groups; or the like.

Also as used herein, the terms “first,” “second,” “bottom,” “top,” andthe like do not denote any order or importance, but rather are used todistinguish one element from another; and the terms “the”, “a” and “an”do not denote a limitation of quantity, but rather denote the presenceof at least one of the referenced item. Furthermore, all ranges recitingthe same quantity or physical property are inclusive of the recitedendpoints and independently combinable. The modifier “about” used inconnection with a quantity is inclusive of the stated value and has themeaning dictated by the context or includes at least the degree of errorassociated with measurement of the particular quantity.

For illustrative purposes, an exemplary open environment CVD device 10is shown in FIG. 1. The CVD device 10 generally comprises a heatingsource 12, a fluid delivery portion 14, a coaxial jet reactor 16, and adeposition portion 18. The fluid delivery portion 14 is in fluidcommunication with the coaxial jet reactor 16, which itself is in fluidcommunication with the deposition portion 18.

The fluid delivery portion 14 includes a carbon-containing precursorreservoir 20, a reducing agent-containing reservoir 22, and an inert gasreservoir 24, all of which are in fluid communication with the coaxialjet reactor 16. The fluid delivery portion 14 may optionally includeflow meters or mass flow controllers 26, 28, 30 to regulate the amountof fluid dispensed by each of the various reservoirs 20, 22, 24,respectively, to the coaxial jet reactor 16. The fluid delivery portion14 may further optionally include a mixer 32 disposed on one side at adownstream junction of the carbon-containing precursor reservoir 20 (oroptional flow meter 26) and the reducing agent-containing reservoir 22(or optional flow meter 28) and the coaxial jet reactor 16 on the otherside. The optional mixer 32 may be used to mix the reducing agent andthe carbon-containing precursor before flowing them downstream towardsthe coaxial jet reactor 16.

The coaxial jet reactor 16 comprises an inner nozzle 36 and an outernozzle 34. In embodiments wherein more than two nozzles are used (notshown), each nozzle is concentric about inner nozzle 36. Regardless ofthe number of nozzles, the outermost nozzle is configured to receive theinert gas and the inner nozzle(s) is configured to receive the reactants(e.g., reducing agent and the carbon-containing precursor) from thefluid delivery portion 14.

The deposition portion 18 comprises an innermost reaction zone 40 and anoutermost zone 38. The number of zones in the deposition portion 18corresponds to the number of nozzles used in the coaxial jet reactor 16.Accordingly, each zone is therefore concentric about the circularinnermost zone 40. Regardless of the number of nozzles/zones, theoutermost zone 38 comprises an inert gas jet from the outermost nozzleof the coaxial jet reactor 16. The thickness of outermost zone 38 (i.e.,the outer diameter minus the inner diameter) must be of sufficient sizeto prevent the introduction of oxygen and/or impurities into any innerreaction zone(s). This outermost zone 38 thus functions as a shield or“curtain”, which peripherally encloses the innermost zone to enable thereactions to occur in an open environment and also eliminates the needfor a vacuum chamber. The ratio of the thickness of the outermost zone38 to all inner zones is greater than or equal to about 0.1:1.

The deposition portion 18 further comprises a substrate 50, a portiononto which the carbon nanotubes are grown. The nanotube growth portionof the substrate 50 is located inside the inner reaction zone(s) 40. Thesubstrate 50 material must be chosen such that it is stable (e.g., doesnot melt, decompose, volatilize, react, or the like) with respect to thethermal energy absorbed from the heating source 12, the reactants, andthe optional catalyst. Suitable substrate 50 materials include quartz,fused quartz, silica, fused silica, sapphire, diamond, or the like. Thesubstrate 50 may have any shape that will allow growth of nanotubesincluding irregular shapes such as flakes as well as regular shapes suchas spheres, rods, sheets, and films.

The deposition portion 18 may optionally include an exhaust 42,downstream of the substrate, to collect of the inert gas, any of thevarious fluids not consumed by the carbon nanotube production, as wellas any material created during the process that does not remain on thesubstrate 50.

The heating source 12 can be any device capable of heating the substrate50 such that the desired deposition temperature is attained once thesubstrate 50 is in the deposition portion 18. In one embodiment, thesubstrate 50 is heated directly inside of the deposition portion 18. Inanother embodiment, the substrate 50 is heated outside of the depositionportion 18 to a temperature slightly above the desired temperature, suchthat any cooling that occurs during its placement into the depositionportion 18 does not reduce the temperature below the desiredtemperature. Alternatively, the substrate 50 can be “pre-heated” outsideof the deposition portion 18 and subsequently heated to the desiredtemperature once inside the deposition portion 18. The heating source12, regardless of where the substrate 50 is heated, can be a resistiveheater, a microwave generator, a flash lamp, an infrared light, a laser,a thermoelectric device, a plasma source, and the like.

In an exemplary embodiment, as depicted in FIG. 1, the heating source isa laser. An advantageous feature of laser induced chemical vapordeposition (LCVD) is that the laser permits greater control and spatialresolution of the deposition temperature than other CVD processes. Inaddition, the deposition temperatures involved in LCVD may be higherthan other CVD processes, which allows for lower defect concentrationsand increased graphitization of the carbon nanotubes.

A laser beam generated by the laser 12 is used to locally heat at leasta portion of the substrate 50 within the deposition portion 18. Thelaser 12 may be any type of laser such as a solid state laser, a gaslaser, an excimer laser, a dye laser, a semiconductor laser, or thelike. The laser beam may be pulsed or may be continuous wave. The choiceof laser 12, and the specific lasing material employed in the laser 12,is based on the absorption characteristics of the substrate 50 and thethermal stability of the carbon-containing precursor. Specifically, thelaser 12 desirably has an emission wavelength at which the substrate 50absorbs and a power level sufficient to provide enough thermal energy toheat at least the portion of the substrate 50 to a temperature greaterthan or equal to the reaction temperature of the carbon-containingprecursor. The appropriate laser may be readily selected by thoseskilled in the art in view of this disclosure without undueexperimentation.

In embodiments where a laser is used as the heating source 12, severaltools may be used to manipulate the laser beam. For example, in order tofocus or tune the laser beam to a specific diameter, the CVD device 10may further include an optical lens 44. The composition of the materialused to make the lens, the shape of the lens, and the distance of thelens from the laser 12 can independently be adjusted to provide adesired laser beam diameter by those skilled in the art in view of thisdisclosure without undue experimentation. For example, the compositionof the material used to make the lens would be selected such that thelens is transparent to the laser beam. The lens shape and distance fromthe laser can be determined using optics equations. Furthermore, asecond, aligning laser (not shown) and/or a laser diode (not shown) maybe used to align the laser beam with the substrate 50. Other componentsthat may be used in conjunction with the laser include a beam splitter(not shown) and/or mirror (not shown) to divide and/or re-focus,respectively, the beam.

Additionally, an optional scattered light absorber 52 may be disposed inthe deposition portion 18 to absorb any portion of the laser beam (orany light beam used to heat the substrate 50) that is not absorbed bythe substrate 50.

The deposition temperature (i.e., temperature of the substrate) may bedetermined using an optional temperature-sensing device 46 that is inthermal communication with the substrate 50. Suitable temperaturesensing devices include thermocouples, pyrometers, and the like.

The open environment CVD device 10 may further comprise a controller 48,such as a computer, in operative communication with the heating source12. In addition, the controller may be used to monitor and/or controlthe optional flow meters 26, 28, 30, the optional mixer 32, the size andflow rate of the jets from the coaxial jet reactor 16, or a combinationcomprising at least one of the foregoing. In embodiments where a laseris used as the heating source 12, the controller may be used to monitorand/or control the optional optical lens 44, the optional second laser,the optional laser diode, the optional beam splitter, the optionalmirror, the optional temperature sensing device 46, or a combinationcomprising at least one of the foregoing.

Producing the carbon nanotubes using the open environment CVD device 10generally comprises heating the substrate or target 50 and at leastpartially thermally decomposing the reactants (e.g., the reducing agentand carbon-containing precursor) in an open environment to depositcarbon nanotubes at an interface between the reactants and a surface ofthe substrate 50. Without being bound by theory, it is believed thatonce the temperature of the substrate 50 exceeds the reactiontemperature of the carbon-containing precursor, the precursordecomposes, in the presence of the reducing agent and in proximity tothe substrate 50, into carbon radicals, which then precipitate to formthe carbon nanotubes.

Carbon nanotube production may be facilitated by having the surface ofthe substrate 50 coated with a nanotube growing catalyst (not shown)prior to the heating of the substrate 50 using the heating source 12.Alternatively, the nanotube growing catalyst can be generated duringdeposition from a catalyst precursor, such as ferrocene. The presence ofthe nanotube growing catalyst increases the rate of nanotube production.The nanotube growing catalyst may be coated onto the substrate 50 usingany known deposition method and may comprise iron, nickel, aluminum,yttrium, cobalt, platinum, gold, silver, palladium, or the like;combinations comprising at least one of the foregoing; and materialcombinations or alloys comprising at least one of the foregoing.

The carbon-containing precursor may be any composition that can at leastpartially thermally decompose into carbon. Furthermore, thecarbon-containing precursor may be a subliming solid, a liquid, or agas. Generally, hydrocarbons of less than about 16 carbon atoms will besuitable, although hydrocarbons with higher numbers of carbon atoms mayalso be suitable, for example, depending on their chemical structure,temperature, and pressure. The hydrocarbons may be of any type,including, for example, alkanes, alkenes, alkynes, alcohols, ethers,esters, carboxylic acids, aldehydes, ketones, carbonates, thiols,amines, and the like. The hydrocarbons may be straight chained,branched, or cyclic.

In one embodiment, the carbon-containing precursor is a mixture ofhydrocarbons. The carbon-containing precursor may be a mixture ofhydrocarbons that are all of the same type or it may contain a mixtureof different hydrocarbons. Further, the mixture may be a mixture ofhydrocarbons all having the same number of carbon atoms such as octane,octene and 1,3-dimethyl-cyclohexane or a mixture of hydrocarbons havingdifferent numbers of carbon atoms such as methanol and butane.

The reducing agent may be hydrogen, ammonia, or a combination comprisingat least one of the foregoing, such as forming gas (non explosivehydrogen and nitrogen mixture).

The inert gas may be nitrogen, helium, neon, argon, krypton, xenon,radon, or a combination comprising at least one of the foregoing.

The volumetric ratio of the carbon-containing precursor to reducingagent may be about 0.01:1 to about 15:1. Specifically, the volumetricratio of the carbon-containing precursor to reducing agent may be about01:1 to about 1:1. Furthermore, the volumetric ratio of the reactants tothe inert gas may be about 0.001:1 to about 10:1. Specifically, thevolumetric ratio of the reactants to the inert gas may be about 0.01:1to about 0.75:1.

In one embodiment, the substrate 50 may be a moving substrate. Owing tothe lack of an enclosed chamber, the substrate may be a continuouslymoving substrate, such as on a conveyor. An exemplary moving substratedevice 100 is shown in FIG. 2. The substrate 50 begins as a rolled sheeton a single feed roll 102 and is fed through the inner reaction zone 40of the deposition portion 18. After the carbon nanotubes are depositedon the portion of the substrate 50 in the inner reaction zone 40, thesubstrate 50 exits the inner reaction zone 40 and is ultimately rolledonto a take-up roll 104. After exiting the reaction zone 40, thesubstrate 50 enters the outer zone 38, where the inert gas jet furtherserves to cool down the heated portion of the substrate 50. In thismanner, ultra-long carbon nanotubes may be grown on the substrate 50 ifthey are grown parallel to the direction of motion of the substrate 50.Alternatively, a larger amount of carbon nanotubes may be produced ifthey are grown perpendicular to the direction of motion of the substrate50.

In another embodiment, the controller 48 controls the position of theapplied heat and/or the position of the substrate 50 using the movingsubstrate device 100. In this manner, the carbon nanotubes may beselectively deposited in specific locations and/or configurations, suchas in a patterned array.

The disclosure is further illustrated by the following non-limitingexamples.

EXAMPLE 1 Carbon Nanotube Production via Laser-Induced Chemical VaporDeposition (LCVD)

A 30 Watt (W) continuous wave carbon dioxide (CO₂) laser (Synrad J48-2W)operating at a wavelength of 10.6 micrometers (μm) was used to heat thesubstrate. The laser beam profile was “TEM_(oo)”, which represents aGaussian distribution. Piano-convex zinc selenide (ZnSe) lenses wereused to focus the laser beam to the desired diameter on the substrate.Proper alignment of the laser beam and the substrate was also performedwith the aid of a low power He—Ne laser beam and a laser diode. Averification and/or realignment of the laser optics was carried out foreach deposition to maintain the consistency of the experimentalconditions. The LCVD device was equipped with a two-color pyrometer formeasuring the deposition temperature. LabVIEW (National InstrumentsCorporation) computer software was used for data acquisition and laserpower control.

With regards to the coaxial jet reactor, the diameters of the inner andouter nozzles are 4.2 and 52.3 mm, respectively. The inert gas wasnitrogen, the carbon-containing precursor was propane (C₃H₈) from Airgaswith 99.95% purity, and the reducing agent was ultra-high purity gradehydrogen. Precision flow meters were used to regulate the flow rate ofthe various gases to the reaction region. The hydrogen and propane weremixed with a mixer. The volumetric flow rates of propane, hydrogen andnitrogen were 0.2, 1.1 and 10 standard liters per minute (SLPM),respectively.

3 millimeter (mm) diameter rods of fused quartz (GE 214 from QuartzPlus, Inc.) were used as the substrates. The substrates were cleanedwith methanol and distilled water and dried with dry air, thensputter-coated with a gold-palladium (Au—Pd) thin film (about 10 nm to100 nm thick depending on sputtering time exposure). In order to convertthe deposited Au—Pd thin film into nanoparticles, each coated substratewas annealed at 1000° C. for 15 minutes in a nitrogen environment at 15Torr. FIG. 3 illustrates environmental scanning electron microscope(ESEM) (Philips 2020 ESEM) images of the Au—Pd nanoparticles for twodifferent film thicknesses under identical annealing conditions. Theaverage particle sizes obtained from films of about 20 nm and about 50nm thickness were about 80 nm (FIG. 3 a) and about 300 nm (FIG. 3 b),respectively. The results indicated that thinner films would give riseto smaller particles sizes. The laser irradiation time for LCVD wasgenerally about ten minutes and was followed by a five-minute coolingperiod. The laser beam diameter was set at 1.8 mm and the laser powerranged from 10-15 W. During each deposition, the temperature history ofthe deposition process was measured by the pyrometer.

The microstructure and chemical composition of the carbon nanotubes wereanalyzed using ESEM and Raman spectroscopy. These characterizationtechniques were used because they were non-destructive. A RenishawRamascope was used to acquire Raman spectra directly from the carbonnanotubes using a 514.5 nm argon ion laser (2.41 eV) at 25 mW as theexcitation source. The argon ion laser beam was focused by a 50×objective lens to illuminate a 1 μm diameter spot on the substrate. Theobtained spectrum contained information representing the averageproperties of the material inside the area of interest. Curve fittingwas applied to the spectra in order to identify relevant Raman peaks. Nosmoothing was applied to the raw Raman data. In addition, transmissionelectron microscopy (JEOL 2010 FasTEM) was used to obtainhigh-resolution images of the carbon nanotubes.

FIG. 4 shows two ESEM images of the carbon nanotubes deposited on afused quartz substrate at a laser power of 10 Watts for a period of 10minutes. These images revealed that the deposited nanotubes were intangled form with no particular growth orientation, and catalystparticles were present along the length of the nanotubes in some regionsof the sample. In addition, nanotubes with small diameter (10-40 nm)tended to grow from the metal catalyst with no metal particles attachedat an end. These observations suggest that both tip-growth andbase-growth modes were present. In tip-growth mode, the catalystparticle is lifted off from the substrate and carried along at the endof the nanotube as the nanotube grows in length. In base-growth mode,the catalyst particles remain adhered to the substrate surface as thenanotubes lengthen. The length of the carbon nanotubes obtained in thisstudy ranged from a few microns to several hundred microns. Longercarbon nanotubes may have been deposited, but the tangling of nanotubesmade it difficult to perform accurate length measurements.

It appeared that the size of the metal catalyst particles determined thediameter of the deposited carbon nanotubes. The average Au—Pd particlesize used in the synthesis of nanotubes shown in FIGS. 3 a and 3 b are80 and 300 nm, respectively. By comparing the diameter of the nanotubes,larger metal particles resulted in larger diameter carbon nanotubes. Theaverage diameter of carbon nanotubes shown in FIGS. 4 a and 4 b areapproximately 50 nm and 220 nm, respectively, which indicates that thesenanotubes were MWNTs. The Raman spectrum of carbon nanotubes obtained inthis study reveal several distinctive peaks located between 100 and 3500cm⁻¹ representing the characteristic Raman peaks of multi-wall carbonnanotubes.

While the disclosure has been described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

1. A device for producing carbon nanotubes, the device comprising: afluid delivery portion comprising a carbon-containing precursorreservoir, a reducing agent reservoir, and an inert gas reservoir; acoaxial jet reactor in fluid communication with the fluid deliveryportion, wherein the coaxial jet reactor comprises an outer nozzleconfigured to receive an inert gas and an inner nozzle configured toreceive a carbon-containing precursor and a reducing agent; a depositionportion in fluid communication with the coaxial jet reactor, wherein thedeposition portion comprises an outer zone configured to receive theinert gas from the outer nozzle, an inner zone configured to receive thecarbon-containing precursor and reducing agent from the inner nozzle,and a substrate having at least a portion within the inner zone, whereinthe outer zone, inner zone and the substrate are in an open environment;and a heating source configured to heat the at least the portion of thesubstrate within the inner zone effective to thermally decompose atleast a portion of the carbon-containing precursor in the presence ofthe reducing agent and produce the carbon nanotubes on the substrate. 2.The device of claim 1, wherein the fluid delivery portion furthercomprises a mixer, a mass flow controller, or both, wherein the mixer isat a junction upstream of the inner nozzle of the coaxial jet reactorand downstream of the carbon-containing precursor reservoir and thereducing agent reservoir, and wherein the mass flow controllerconfigured to regulate an amount of fluid dispensed by thecarbon-containing precursor reservoir, reducing agent reservoir, orinert gas reservoir.
 3. The device of claim 1, wherein a ratio of athickness of the outer zone of the coaxial jet reactor to the inner zoneof the coaxial jet reactor is greater than or equal to about 0.1:1. 4.The device of claim 1, wherein the deposition portion further comprisesan exhaust, a scattered light absorber, or both.
 5. The device of claim1, wherein the heating source is a laser.
 6. The device of claim 1,further comprising an optical lens, an aligning laser, a laser diode, abeam splitter, a mirror, a temperature-sensing device, or a combinationcomprising at least one of the foregoing.
 7. The device of claim 1,further comprising a controller in operative communication with theheating source, mass flow controller, mixer, optical lens, aligninglaser, laser diode, beam splitter, mirror, temperature sensing device,substrate, or a combination comprising at least one of the foregoing. 8.The device of claim 1, wherein the substrate is a moving substrate. 9.The device of claim 1, wherein a surface of the substrate comprises ananotube growing catalyst.
 10. The device of claim 1, wherein avolumetric ratio of the carbon-containing precursor to the reducingagent is about 0.01:1 to about 15:1.
 11. The device of claim 1, whereina volumetric ratio of the carbon-containing precursor and the reducingagent to the inert gas is about 0.001:1 to about 10:1.
 12. A device forproducing carbon nanotubes, the device comprising: a fluid deliveryportion comprising a carbon-containing precursor reservoir, a reducingagent reservoir, an inert gas reservoir, a carbon-containing precursormass flow controller, a reducing agent mass flow controller, an inertgas mass flow controller, and a mixer at a junction downstream of thecarbon-containing precursor reservoir and the reducing agent reservoir,and a coaxial jet reactor in fluid communication with the fluid deliveryportion, wherein the coaxial jet reactor comprises an outer nozzleconfigured to receive an inert gas and an inner nozzle configured toreceive a carbon-containing precursor and a reducing agent; a depositionportion in fluid communication with the coaxial jet reactor, wherein thedeposition portion comprises an outer zone configured to receive theinert gas from the outer nozzle, an inner zone configured to receive thecarbon-containing precursor and reducing agent from the inner nozzle, asubstrate having at least a portion within the inner zone, a nanotubegrowing catalyst disposed on a surface of the substrate, an exhaust, anda scattered light absorber, wherein the outer zone, inner zone,substrate, nanotube growing catalyst exhaust, and scattered lightabsorber are in an open environment; a laser, wherein a beam produced bythe laser is configured to heat the at least the portion of thesubstrate within the inner zone effective to thermally decompose atleast a portion of the carbon-containing precursor in the presence ofthe reducing agent and produce the carbon nanotubes on the substrate;and a controller in operative communication with the laser,carbon-containing precursor mass flow controller, reducing agent massflow controller, inert gas mass flow controller, mixer, substrate or acombination comprising at least one of the foregoing.
 13. The device ofclaim 12, wherein a ratio of a thickness of the outer zone of thecoaxial jet reactor to the inner zone of the coaxial jet reactor isgreater than or equal to about 0.1:1.
 14. The device of claim 12,further comprising an optical lens, an aligning laser, a laser diode, abeam splitter, a mirror, a temperature-sensing device, or a combinationcomprising at least one of the foregoing.
 15. The device of claim 14,wherein the controller is further in operative communication with theoptical lens, aligning laser, laser diode, beam splitter, mirror,temperature sensing device, or a combination comprising at least one ofthe foregoing.
 16. The device of claim 12, wherein the substrate is amoving substrate.
 17. A method for growing carbon nanotubes, comprising:heating at least a portion of a substrate in an open environment;forming a first jet of reactants comprising a carbon-containingprecursor and a reducing agent, wherein the first jet is surrounded by asecond jet of inert gas that is effective to protect the reactants fromthe open environment; thermally decomposing at least a portion of thecarbon-containing precursor in the presence of the reducing agent inproximity to the heated substrate; and growing the carbon nanotubes onthe at least the portion of the substrate.
 18. The method of claim 17,further comprising mixing the carbon-containing precursor with thereducing agent prior to the forming the jet of reactants in an openenvironment.
 19. The method of claim 17, further comprising disposing ananotube growing catalyst onto the at least a portion of a substrate.20. The method of claim 17, further comprising moving the substratecontemporaneously with the growing.